According to Digitimes, the X38 chipset is still set for a September launch and to our knowledge the launch date is still the 24th. Motherboard partners should have received delivery of chipsets earlier than that, so production of motherboards should already be up and running. However, the manufacturers we've talked to are concerned about the small amounts of samples they've received so far for their R&D departments.
It's apparently quite complicated to build boards based on the X38 chipset, partly due to its hot nature, hence the integrated heat spreader and partly because of some issues that have appeared. One of the problems is that the traces between the chipset and the DDR3 memory slots have to be much shorter than on the P35 chipset and this makes it more difficult to design the boards.
We've also been told that Intel didn't send out any reference samples to its board partners, which makes it harder for them to make their own designs, especially as there seems to be a fair few bugs, sorry, errata's in the X38 chipset, which some manufacturers are having problems with. Hopefully all these issues will be resolved before retail products appear.
The X48 is apparently real and it's meant to support 1,600MHz FSB, the X38 is stuck at 1,333MHz officially. The X48 will also have native support for 1,600MHz DDR3 memory, again something that the X38 won't have. The two are apparently pin compatible, so there's no need for the motherboard manufacturers to change their board designs.
You can find the Digitimes story here